The present invention relates to NFC cards (Near Field Communication), and more particularly NFC cards intended to be inserted into a terminal such as a mobile phone. The present invention also relates to a method for performing a contactless or near field communication between an NFC card and an external NFC device.
To allow a mobile phone not comprising any contactless communication interface to communicate with an external NFC device, contact and contactless dual interface NFC cards intended to be inserted into the phone have been developed. These cards are for example of the UICC card type (Universal Integrated Circuit Card) such as NFC SIM (Subscriber Identity Module), or of the NFC SD type (Secure Digital). An NFC SIM card comprising contact pads, a microprocessor, an NFC module, and an antenna coil has already been provided. This card can perform contact communications with the mobile phone through the contact pads and an NFC communication with an external NFC device through the antenna coil.
When the card and the external NFC device are placed sufficiently close to each other, the antenna coil of the card is inductively coupled to an antenna coil of the external NFC device, and data can be exchanged using conventional NFC techniques such as those defined by the standards ISO 14443, ISO 15693, and Sony Felica®.
In most applications, the external device emits a magnetic field whereas the NFC card is passive and sends data by load modulation. To that end, the antenna coil of the card is associated with passive components (e.g. capacitors) to form an antenna circuit tuned to a working frequency of the external device, for example 13.56 MHz.
FIG. 1 schematically shows a portable terminal HD1 comprising a main processor BBP. An NFC card referred to as NFSE is inserted into the terminal HD1 and connected by a contact interface and an electrical link B1 to the processor BBP. The card NFSE comprises an antenna circuit AC to communicate with an external NFC device ED. The link B1 may comply with the standard ISO 7816.
This solution is not satisfactory because portable terminals generally comprise metal parts or metal components, for example a printed circuit board. When an NFC card is inserted into such a terminal, such metal parts or components reduce the inductance of the antenna coil, thereby altering the tuning frequency of the antenna circuit and reducing the maximum communication distance between the NFC card and the external device ED.
It is difficult for NFC card manufacturers to know in advance the conditions in which an NFC card will be used, i.e. what the metallic environment of the card will be and how the NFC card will be arranged in relation to the printed circuit board, in particular whether its longitudinal axis will be parallel or perpendicular to an edge of the printed circuit board. The card location may significantly vary from terminal to terminal. The location may be more or less electromagnetically shielded, and the terminal may comprise a variable number of metal parts near the card. Consequently, the maximum possible communication distance from the card greatly depends on the card environment and may significantly vary depending on the terminal into which the card is inserted. In addition, the magnetic field emitted by the external device induces eddy currents in the metal parts, which create a counter magnetic field that tends to neutralize the magnetic field, thereby further reducing the maximum communication distance between the NFC card and the external device.
There are also mobile phones equipped with an NFC module to communicate with an external NFC device. In this case, the SIM card inserted into the phone does not need to comprise a contactless interface. Thus, FIG. 2 schematically shows a terminal HD2 comprising a main processor BBP and an NFC module referred to as NFCC connected to an antenna circuit AC1 and connected through a link B2 to the processor BBP. A SIM card referred to as SE is inserted into the terminal wherein it is connected through a contact interface and an electrical link B1 to the processor BBP. The SIM card may also be connected to the NFC module through a link B3.
This solution has the advantage of offering an antenna circuit for contactless communications, here the circuit AC1, which may be installed in the terminal and adapted to the metal parts present therein. The antenna circuit AC1 may therefore offer a maximum communication distance.
However, users of the terminal HD2 may be required to insert into their terminal a card having its own contactless interface, such as the card NFSE in FIG. 1. This case schematically shown in FIG. 3 may arise in particular when a user already having an NFC SIM card buys a new phone having its own NFC module. The result is that when the terminal is brought near an external NFC device, a conflict may occur between the card NFSE and the module NFCC. Indeed, the card NFSE and the module NFCC may simultaneously be called by an external NFC device which will see two different NFC devices in its field.
To solve this problem, the document WO 2011/079606 provides for adapting the main processor BBP of the terminal so that it sends the NFC SIM card a switching command so that it does not use its NFC interface terminal to perform contactless communications, but uses that of the terminal or the NFC module instead. This solution also implies that mobile phone manufacturers and NFC SIM card manufacturers, which are different, agree on the definition and processing of such switching commands.
In addition, the contactless interface of the NFC SIM card may in some cases offer a communication distance greater than that of the module NFCC. It may then be preferred to use the communication interface having the greatest communication distance. It is not possible to know in advance which contactless interface will have the greatest communication distance. Indeed, that of the contactless interface of the card NFSE depends on its position in the terminal HD2 and on the configuration of the metal parts present in the terminal HD2, which substantially vary from one model of terminal to another. In addition, the card NFSE may start a communication with an external NFC device ED without involving the processor BBP. The latter cannot therefore determine the contactless interface having the greatest communication distance, and thus select a contactless interface according to the communication distance.
In addition, if the card NFSE is configured to start or respond to a contactless communication request using its own contactless interface, the module NFCC must not respond to the signals it receives through its contactless interface, to avoid conflicts.
There is therefore a need to implement a near field communication method between a terminal comprising an NFC module and an NFC SIM card, and an external NFC device, avoiding the risks of conflict between the NFC module and the NFC SIM card. There is also a need to be able to choose the near field communication interface having the greatest communication distance or the best quality. It is also desirable that this communication method remain compatible with a terminal equipped with a SIM card, but comprising a single contactless interface, provided either in the SIM card inserted into the terminal, or in an NFC module of the terminal.